Coaxial cable switch



7 July 28, 1959' E. S. BURGESS COAXI'AL CABLE SWITCH Filed Jan. 24, 1958IN VEN TOR. fowl/e0 5 fiulfifas ATM/Mfr COAXIAL CABLE SWITCH Edward :S.Burgess, Rutherford, NJ. Application-January 24, 1958, Serial'N'o.711,106

9 Claims. or. 200-87) "This invention relates to high frequencyelectrical circuits, particularly to a switching circuit therefor, andhas "for its primary object to provide a mechanism for switching fromone coaxial cable to another coaxial cable, .whereby the transmissionefficiency of said interconnected cables through said mechanism ismaintained at substantially the same level as in the cables.

It is important, particularly in high frequency circuits, that theimpedance of cables and interconnected circuits be equal. As is wellknown, a mismatch in impedance produces a reflected wave or bump havinga magnitude determined bylthe extent of impedance mismatch. While thecoaxial cables themselves have predetermined impedances that are readilymatched, it has been found that irregularities are introduced into thecircuit at switching points of the cables with consequent disturbancesand lowered efficiency.

It is, therefore, another object of the invention to overcome the abovedisadvantages and to provide a constant impedance coaxial switch.

It is still another object of the invention to provide a switch that hasa constant impedance regardless of mechanical tolerances in theconstruction of the parts thereof.

.It is a further object of the invention to provide a coaxial cableswitch free of connectors, whereby coaxial cables of any length may bedirectly terminated in the switch and conductors of the cables used asswitching components.

Yet a further object of the invention is. to provide such a constantimpedance switch which is simple and economical in construction andpractical and reliable in operation.

Other and further objects will be obvious upon an understanding of theillustrative embodiment about to be described, or will be indicated inthe appended claims, and various advantages not referred to herein willoccur .to one skilled in the art upon employment of the invention inpractice.

A preferred embodiment of the invention has been chosen for purposes ofillustration and description and is shown in the accompanying drawing,forming a part of the specification, wherein:

Fig. 1 is a front elevational view of a coaxial cable switch of theinvention showing three coaxial cables directly terminated in the switchbody and an electrical relay assembled thereto,

Fig. 2 is a sectional view taken along line 2-2 of Fig. l in thedirection of the arrows showing the detailed construction of the switchwith the inner conductor of the coaxial cable functioning as a switchingcontact,

Fig. 3 is a schematic view of the switch arrangement.

Referring 'now to the drawing, particularly Figs. 1 and 2., there isshown a switch body of any suitable conductive material, such asaluminum because of its lightness in weight, having a pair of openended, intersecting grooves. 11, 12 formed therein. Both grooves .are ofthe samedepth and width, about A inch, for example, for use with a 52ohm cable, groove 12 being off center Patented July .28, 1959 f. we

and adjacent the front edge 14 of the body and extending betweenside-edges 16, 17, and groove 11 being centrally disposed between sideedges 16, 17 and extending between front edge 14 and rear edge 18. Asseen in Fig. 2, the intersecting grooves are in the shape of an inverted'T, groove 12 containing two spaced coaxial cable terminations 19, '21and groove 11 containing a third coaxial cable termination 22.

The coaxial cables are conventional, each consisting of an outerinsulating cover 24, an outer mesh conductor 26, a centrally disposed,inner conductor 27, and an insulating layer '28 between the twoconductors '26, 27. It is to be noted that the coaxial cables 19, 21,and 22 are terminated directly in the grooves of the switch block, theusual connectors being eliminated, and the inner conductors 27 beingutilized as switching contacts, as will appearhereinafter. Inotherwords, the coaxial cable conductors are used as integralpartsof theswitch and, by eliminating intermediate connectors, avoid troublesomeimpedance mismatch.

For terminating the cables in the switch body 10, each cable-is strippedto permit the inner conductor 27 to project a short distance, as seen inFig. 2, and a sheathed contact piece 29 is rigidly secured thereto. Thecontact piece 29 is only long enough to befastened to the innerconductor 27, so that the same, constant impedance of the coaxial cableis maintained within the switch block. The outer insulation 24 is thenremoved for a slightly greater distance to expose the outer, braidedconductor 26 and around this-latter conductor a collar 31 of conductivematerial, preferably brass, having a slot 30 on its face and having asquare, outer configuration is rigidly secured, as by solder, the slot30 assisting in making a good soldered connection. The cross-sectionaldimensions of each collar 31 are of substantially the same width and.depth as the groove in which it is slid'able, in this example beingabout A 'inch for a 52 ohm coaxial cable. To adjustably secure eachcollar 31 and associated cable ina fixed position within the switchblock, a set screw 32 for each of cables 19, 21 adapted to penetrateinto groove 12 and a set screw 33 for cable 22 adapted to penetrate intogroove 11 are provided. As is evident, the set screws 32, 33 are in meshengagement with threaded openings 34 in the body 10. Thus it seen thatthe outer conductors of all three cables are interconnected through theswitch body 10.

The sheathed contact piece 29 of the central conductor "27 for cable 22is shown slotted and in the slot is rigidly secured one end of a short,flat spring 36, preferably of beryllium copper, having a contact 37intermediate its ends adapted to alternately engage the contacts 29 ofcables '19, 21. In this example 'of a switch for a 52 ohm cable thespring 36 is about inch in length between slotted contact 29 and contact37, inch in width and 0.005 inch thick, whereby a capacitance of about29 micromicrofarads .per inch is maintained in the cavity formed ingroove 11 and occupied byspring'36. At this point it may be mentionedthat the shorter the length of spring 36 the less likelihood there is ofimpedance mismatch between cable 22 and either of cables 19 and 21.

The spring 36 is shown initially biased to engage one of said contactpieces in order to provide a continuous connection, as between cable '22and cable 21 in the present illustration, transfer of contact 37 fromcable 21 to cable 19 being produced by electromechanical means, as willappear hereinafter. All three contact pieces '29 are held firmly to therespective outer conductors by insulating material 38, whichalsorigidifie's the central conductors '27 and assures good engagementbetween contacts 7 M 2 i In view of the'lzore'goingconstructiomaconstant 'ele'ctrical'impedance is maintained in the switchunit. This is brought about primarily by terminating each coaxial cabledirectly in the switch, so that the sheath contact pieces 29 of opposingcables 19, 21 areat a relatively :short distance apart and the spring 36forinterconnecting cable 22 to either of cables 19, 21 is alsorelatively short. The cavity in which the spring 36 is located is alsorelatively short and is dimensioned to have the same electrical capacityper unit length as the coaxial cable terminals. The inherent shortnessof the elements also enables the switch to be useful at shorterelectric-wave lengths, since any variable impedance bump in an otherwiseconstant impedance circuit has less detrimental effect on the wavelength, if the impedance bump is short in length compared with theassociated electric wave length. As seen in Fig. 1, a cover 39 having aslot 41 in registration with the front end of groove 11 is provided asan upper closure for the switch body 10, the cover being secured to thebody by screws 42 freely passing through openings 43 in the body andmeshing with threaded openings 44 in the cover. On top of the cover isrigidly mounted a bracket 46 and to this bracket is fastened anelectrical relay 47 having a winding 48, armature 49, and windingterminals 51. The armature 49 is shown formed with a depending arm 52 towhich is rigidly secured a further depending arm 53, preferably of wire,having a right angle bend therein and being adapted to be movablydisposed in said slot 41 and groove 11. A short tubular piece 54 ofinsulating material is shown around the lower end of the wire arm 53 toinsulate it from the free end of the transfer spring 36 of the cable 22.

The operation of the switch will now be described. The coaxial cableswith the hereinbefore described terminations are initially placed intheir respective grooves and the collars 31 are slid to their properpositions in the grooves, after which set screws 32 and 33 are turned tosecure them in place. Assuming that the transfer spring 36 is biased tothe right, as viewed in Figs. 2 and 3, with contact 37 in engagementwith contact piece 29 of cable 21, communication may then be had overboth cables 21 and 22. To change the circuit from cable 21 to cable 19it is merely required to move transfer spring 36 to the left. For thispurpose any suitable source 56 (Fig. 3) of electrical energy may be usedand by closing switch 57 a simple energizing circuit for relay 47through winding 48 is established. Upon energization of relay winding 48armature 49 is attracted thereto and its depending arm 53 with insulatedend piece 54 is moved to the left, as viewed in Figs. 1, 2, and 3, sothat contact 37 separates from contact 29 of cable 21 and engagescontact 29 of cable 19. Communication over cables 19 and 22 may be hadas long as relay 47 is operated, opening of switch 57 de-energizing therelay and causing the armature 49 to retract to its normal position,after which transfer spring 36 also retracts to its initially biasedposition to reestablish the originally described connection betweencables 22 and 21.

From the foregoing description, it will be seen that the presentinvention provides a simple, economical, and highly practicable switchwhich offers a constant impedance to interconnected coaxial cables,particularly since the cable conductors are utilized as component partsof the switch and since the transfer spring, cavity containing thetransfer spring, and spacing between opposing cable conductors are allrelatively short to meet the required impedance value. While the 52 ohmcoaxial cable example has been described in detail hereinbefore, it is,of course, understood that applicant is not limited to this example.

As various changes may be made in the form, construction, andarrangement of the parts herein, without departing from the spirit andscope of the invention and without sacrificing any of its advantages, itis to be under- 4 stood that all matters are to be interpreted and notin any limiting sense.

What is claimed is:

1. A switch unit comprising a body of conductive material having a pairof intersecting grooves each of equal depth and width and having a coverover said grooves forming a cavity in one of said grooves, a pair ofcoaxial cables of predetermined characteristic impedance each having acentral conductor and a spaced, sleeve conductor surrounding the centralconductor, said cables having respective ends thereof disposed in saidgrooves, a contact at the end of one of said central conductors, a flat,movable element of conductive material having one end thereof secured tothe other of said central conductors disposed in said one of saidgrooves within said cavity and having the other end thereof biased intoengagement with said contact at the end of said one central conductor,said movable element being proportioned to the cavity dimensions toproduce a constant capacitance per unit length of the cavity, wherebythe characteristic impedance along said cavity is maintainedsubstantially equal to the characteristic impedance of said coaxialcables, means for securing said sleeve conductors in said grooves tosaid body, whereby said body constitutes a common outer conductor forsaid cables, and means for separating said movable element fromengagement with said contact.

2. A switch in accordance with claim 1, wherein said cavity isrectangular in longitudinal section.

3. A switch in accordance with claim 1, wherein said grooves are atright angles with respect to each other.

4. A switch unit comprising a body of conductive material having a pairof intersecting grooves each of equal depth and width and having a coverover said grooves forming a cavity in one of said grooves, a pair ofcoaxial cables of predetermined characteristic impedance each having acentral conductor and a spaced, sleeve conductor surrounding the centralconductor, said cables having respective ends thereof disposed in saidgrooves, a contact at the end of one of said central conductors, aflat,.movable element of conductive material having one endthereofsecured to the other of said central conductors disposed in said one ofsaid grooves within said cavity and the other end thereof biased intoengagement with said contact at the end of said one central conductor,said movable element being proportioned to the cavity dimensions toproduce a constant capacitance per unit length 'ofthe cavity, wherebythe characteristic impedance along said'cavity is maintainedsubstantially equal to the characteristic impedance of said coaxialcables, a collar of conductive material connected to each of said sleeveconductors, means for securing said collars in said grooves to saidbody, whereby said body constitutes a common outer conductor for saidcables, and electrical means for separating said movable element fromengagement with said contact.

5. A switch in accordance with claim 4, wherein said electrical means isconstituted by a relay having attached to its armature an insulated endportion adapted to disengage the flat element from the contact.

6. A switch in accordance with claim 4, and insulating means interposedbetween said contact and said sleeve conductor for stiffening said onecentral conductor.

7. A switch unit comprising a body of conductive material having a pairof intersecting grooves each of equal depth and width and having a coverover said grooves forming a cavity in one of said grooves, three coaxialcables of the same predetermined characteristic impedance each having acentral conductor and a spaced, sleeve conductor surrounding the centralconductor, said cable having respective ends thereof disposed in saidgrooves with one of said cables disposed in said one groove and theremaining two of said cables oppositely spaced in the other of saidgrooves, a contact at the end of each of said centralconductors of saidremaining two cables, a flat,

as illustrative movable element of conductive material having one endthereof secured to the other of said central conductors disposed in saidone of said grooves within said cavity and having the other end thereofbiased into engagement with said contact at the end of one of saidcentral conductors of said remaining two cables, said movable elementbeing proportioned to the cavity dimensions to produce a constantcapacitance per unit length of the cavity, whereby the characteristicimpedance along said cavity is maintained substantially equal to thecharacteristic impedance of said coaxial cables, a collar of conductivematerial connected to each of said sleeve conductors, means for securingsaid collars in said grooves to said body, whereby said body constitutesa common outer conductor for said three cables, and electrical means fortransferring said movable element from said contact at the end of saidone central conductor to the other contact at the end of the othercentral conductor of said remaining two cables.

8. A switch unit in accordance with claim 7, wherein said electricalmeans is constituted by a relay having attached to its armature aninsulated end portion adapted for transferring said flat element fromengagement with one to the other of said contacts of said centralconductors of said remaining two cables.

9. A switch in accordance with claim 7, and insulating means interposedbetween said contact and said sleeve conductor of each of said remainingtwo cables for stif- 1 fenting said central conductors thereof.

References Cited in the file of this patent UNITED STATES PATENTS2,472,274 Beleskas June 7, 1949 2,478,781 Reinschmidt Aug. 9, 19492,560,561 Ellis et a1. July 17, 1951

